This application is based upon and claims the benefit of Japanese Patent Applications No. 11-279301 filed on Sep. 30, 1999, and No. 11-284218 filed on Oct. 5, 1999, and No. 11-288398 filed on Oct. 8, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to an electronic control unit for drive-controlling an outside control object, and a manufacturing method thereof.
2. Description of the Related Art
There have been known electronic control units (for example electronic control units for mounting in vehicles, which perform engine control or transmission control) for supplying electrical power to and thereby driving outside control objects (for example various actuators such as electromagnetic solenoids) and controlling their operation.
This kind of electronic control unit, for example as shown in FIGS. 1A and 1B, is made by housing a connector 102, a control processing element 103 and drive elements 105 in a box 107. The control processing element 103 performs computational processing on the basis of signals inputted from outside via the connector 102 and outputs control signals. The control processing element 103 is for example a CPU or a microcomputer. The drive elements 105 are for being driven by control signals from the control processing element 103 and supplying power to outside control objects, and are for example power transistors or power ICs.
In this kind of electronic control unit, from the point of view of productivity improvement and cost reduction, the control processing element 103 and the drive elements 105 have been mounted on the same circuit board 109 as shown in FIGS. 1A and 1B. However, the drive elements 105 handle large currents (i.e. electrical powers) compared to the control processing element 103 and so on, and produce a large amount of heat. On the other hand, the control processing element 103, which performs various computational processing, readily suffers influences of heat, and consequently there is a possibility of heat produced by the drive elements 105 excessively raising the temperature of the control processing element 103 and making its operation unstable.
Generally, because the circuit board 109 on which the control processing element 103 and the drive elements 105 are mounted uses a board made of resin having a relatively low thermal conductivity among the various circuit boards, the positional relationship between the two has been considered for example by separating the control processing element 103 and the drive elements 105 as much as possible on the board. By this being done, it has been made difficult for heat produced by the drive elements 105 to reach the control processing element 103. Incidentally, FIG. 1A shows the construction of the electronic control unit as seen from a direction parallel with the board face of the circuit board 109, and FIG. 1B shows the electronic control unit as seen from a direction perpendicular to the board face of the circuit board 109.
However, in electronic control units of recent years, due to complicated and multifunctionalized control content, the increase in number of the drive elements 105 and the increase in power handled by the drive elements 105 have progressed. Further, along with this the amount of heat produced in the drive elements 105 is in an increasing trend. In this case, it is conceivable to suppress thermal influences on the control processing element 103 by making the circuit board 109 larger and further separating the control processing element 103 from the drive elements 105. However, when the space for mounting the electronic control unit is restricted (for example in cases such as when the electronic control unit is to be mounted in a vehicle), there is a limit from the point of view of saving space. Further, when the area of the circuit board 109 is made large, the manufacturing yield of the circuit board 109 deteriorates, and as a result the manufacturing cost of the electronic control unit can be increased.
Because of this in electronic control units of recent years it has been becoming not easy to suppress thermal influences affected on the control processing element 103 by heat produced in the drive elements 105. Further, as the amount of heat produced in the drive elements 105 increases, it may exceed the limit of the thermal radiation capacity in the electronic control unit. In such case, heat produced in the drive elements 105 is not sufficiently dissipated, and not only the control processing element 103 but also the operation of the drive elements 105 may become unstable.
The present invention has been made in view of the above problems. An object of the present invention is, in an electronic control unit, to improve operational reliability against heat while suppressing increase in size and increase in manufacturing cost of the electronic control unit.
According to the present invention, in an electronic control unit, a drive circuit board holding a drive element for supplying power to an outside control object is disposed on a drive circuit board, and a control processing element for outputting a control signal to the drive element to control the outside control object is disposed on a control circuit board. A connector through which a signal is inputted into the control processing element and the power is supplied to the outside control object is further disposed on the control circuit board. The drive circuit board and the control circuit board are disposed in a box to face each other and connected by a connecting wire.
Preferably, the connecting wire is connected to the control circuit board at a bonding portion in a vicinity of the connector. The connecting wire can be bonded to mutually facing end parts of the control circuit board and the drive circuit board, be bent to form a gap with a wall of the box, and have a length that allows the control circuit board and the drive circuit board to be lined up in an identical plane without an overlap.
Preferably, the control processing element and the drive element are disposed at opposite sides to each other with a plane interposed therebetween, the plane being approximately perpendicular to an inner wall of the box on which the drive circuit board is disposed.
According to the present invention described as above, heat generated in the drive element is suppressed from being transferred to the control processing element, and the operational reliability against heat of the electronic control unit is improved while suppressing increase in size and increase in manufacturing cost.